The method of objectively evaluating an image quality of a video picture is roughly divided into three kinds. A first evaluation method is a method of directly comparing an original image with a deteriorated image, thereby to evaluate the image quality. A second evaluation method is a method of evaluating the image quality only from the deteriorated image. A third evaluation method is a method of forwarding a feature of the original image, and evaluating the image quality from this feature and the deteriorated image.
While with the first evaluation method, a specific method of evaluating a perceptual video quality is recommended by ITU-T as described in Non-Patent document 1, the first evaluation method necessitates the original image (the image that is obtained before transmission) in a reception apparatus side for making an evaluation when an evaluation of the image quality of the transmitted image is attempted. However, it is impossible to transmit the original image to the reception apparatus side with the image quality thereof kept as it stands due to an upper limit of a communication band of a transmission path. Thus, a reception terminal side cannot evaluate the image quality of the transmitted image by employing the first evaluation method.
Further, the second evaluation method is an ideal method because the reception apparatus side can evaluate the image quality independently; however, the second evaluation method is difficult to realize because it is hard to separate an original feature of the image from the feature generated due to the deterioration of the image quality when an evaluation of the image quality of the transmitted image is attempted.
On the other hand, there is no necessity for transmitting the original image itself in the third evaluation method because the feature of the original image is transmitted to the reception apparatus side, and the image quality of the transmitted image is estimated based upon this feature. Thus, when the appropriate feature can be transmitted, the evaluation of the image quality, which is performed at a low-bit rate, and yet is highly precise, can be expected.
For example, in Patent document 1, the transmitted image quality monitoring apparatus for evaluating the image quality of the transmitted image by employing the third evaluation method is described. The transmitted image quality monitoring apparatus described in the Patent document 1 divides an input image into blocks each having an arbitrary size, subjects videos within the block to an orthogonal transform, extracts arbitrary orthogonal-transformed frequency component values, and transmits them as a feature. Additionally, in the Patent document 1, the method of, after multiplying the signals in the blocks by a sequence (PN sequence) in which +1 and −1 are generated at random and performing whitening for them, subjecting them to an orthogonal transform, extracting arbitrary frequency components, and transmitting them as a feature is disclosed. The reception apparatus side evaluates the image quality by calculating an error of this frequency component between the original image and the transmitted image, and estimating an error of the entirety of the image.
Patent document 1: JP-P2003-9186A
Non-Patent document 1: ITU-T Recommendation, “J.144 Objective perceptual video quality measurement techniques for digital cable television in the Presence of a full reference”, ITU-T Recommendation, 2004